Summary of Work: The goal of these studies is to investigate the molecular signal tranduction pathway that recognizes DNA strand breaks and causes cells to cease proliferation, either as a consequence of exposure to environmental carcinogens or as part of the normal program of cellular ageing (senescence). One gene product that seems to be required for a proper cellular reponse to multiple forms of DNA damage that occur throughout the cell's proliferative cycle is the product of the gene responsible for the autosomal recessive disorder ataxia telangiectasia (AT), referred to as ATM for AT Mutated gene.The role of the ATM protein in transmitting signals that result in the inhibition of cyclin/cdk protein kinase complexes is being investigated. We have raised antisera in rabbits to three peptides whose sequences correspond to predicted sequences in the carboxyl-terminal half of the ATM protein and three peptide sequences corresponding to regions in the amino terminal region. We are characterizing these antisera as well as three antisera raised by our collaborator Dave Hill of Oncogene Research. We have been successful in reproducibly detecting the 350 kDa ATM protein in extracts from NHF and HeLa cells that is lacking in fibroblasts from AT patients. The ATM protein is a nuclear protein whose levels of expression do not vary over the cell cycle or in response to DNA damaging agents. Studies are underway to investigate the function of this cancer susceptibility gene product in response to DNA damage and ageing. The results of these studies will contribute to a better understanding of the normal molecular events regulating cellular senescence and cell cycle checkpoint delay. In addition, these studies hold the potential for proving insight into mechanisms of action of certain NTP compounds, in particular those compounds that have been classified as non-genotoxic carcinogens.